No regrets here, but I did use Google Code a fair bit prior to GitHub and I had an experience that made me think maybe Google regretted that product in some ways.
Around 2005-6 I wrote a Mac OS X client for Xbox Live. The idea was I wanted notifications on my computer when my friends came online and started to play certain games, so I could turn on my Xbox and join them. This is a feature of the Xbox mobile app today of course, but back then all you could do was either be on the Xbox or sit around refreshing a web page, so the app was useful. I published the source and the binaries on Google Code, partly because I just wanted to share the app for free, and partly because I wanted to be transparent that I was handling the Xbox login credentials safely.
One day the app blew up and got a lot of coverage in tech news and link aggregators (like Digg, haha) and I suddenly had a ton of users. Eventually I figured out why. It wasn't that my app was so great exactly, but rather the idea that Google was writing a Mac client for Xbox made a great tech news story. However, that part of the story wasn't true, the project had nothing to do with Google, I was just hosting it on Google Code because it was at the time the most convenient place for a small open source project.
The episode made me wonder how often that happened. How many other projects on Google Code became part of a news cycle because people misinterpreted them as being written or endorsed by Google? Was that part of why Google Code was shut down?